1. Field of the Invention
This invention relates to oxidation dyes for dyeing keratin fibers, more particularly human hair, based on indoline derivatives, more particularly 5,6-dihydroxyindoline, oxidative color development taking place by oxidation with atmospheric oxygen in the presence of lithium, magnesium, calcium, aluminium or zinc salts as catalysts without the use of additional oxidizing agents.
2. Statement of Related Art
By virtue of their intensive colors and good fastness properties, so-called oxidation hair dyes play a prominent part in the dyeing of keratin fibers, for example wool, fur or hair. Oxidation hair dyes contain oxidation dye precursors in a cosmetic carrier. Primary intermediates and couplers are used as the oxidation dye precursors. The primary intermediates form the actual dyes with one another or by coupling with one or more coupler components under the influence of oxidizing agents, generally H.sub.2 O.sub.2.
Para-aminophenol and para-phenylenediamine derivatives are normally used as the primary intermediates. Meta-phenylenediamine derivatives, naphthols, resorcinol derivatives and pyrazolones are used as so-called couplers.
Dyes for dyeing keratin fibers are required to show favorable dyeing properties such as, for example, good absorption onto the fibers at low temperatures. The color obtained must exhibit good fastness properties. On the other hand, however, the dye must be both toxicologically and dermatologically safe, above all when human hair is to be dyed. Unfortunately, the para-aminophenol and para-phenylenediamine derivatives present in conventional oxidation dyes can cause sensitization and allergies in certain people. Accordingly, there has been no shortage of attempts to replace para-aminophenol and para-phenylenediamine derivatives by other, if possible "nature-identical" oxidation dye precursors. Indole derivatives, the basic structural elements of the natural melanin dye present in hair, are a possibility in this regard.
Unfortunately, many indole derivatives are unsuitable for use in commercial hair dyes on account of their excessive sensitivity to oxidation and the resulting handling problems.
The indoline derivatives described in DE-A 40 16 177 are a promising alternative. They are stable in storage and form the corresponding indole derivatives "in situ" by oxidation. The indole derivatives then polymerize to form the actual dye.
H.sub.2 O.sub.2 is normally used as the oxidizing agent. However, H.sub.2 O.sub.2 leads to changes in the original properties of the hair. Thus, H.sub.2 O.sub.2 -treated hair is drier, more brittle and more difficult to comb. It is more porous and, hence, more sensitive to the influence of moisture and takes longer to dry, its resistance and tensile strength are reduced. Accordingly, efforts are being made to develop hair dyes without H.sub.2 O.sub.2 or other oxidizing agents and to use atmospheric oxygen for the oxidative dyeing of hair. However, the complete absence of H.sub.2 O.sub.2 leads to unsatisfactory dyeing results. Thus, the intensity of color obtainable where indoline derivatives are used as oxidation dye precursors is very poor.
EP-A 0 462 857 describes inter alia hair dyeing processes using indolines as oxidation dye precursors, the indolines being oxidized with atmospheric oxygen in the presence of catalytic quantities of metals of the 3rd to 8th secondary groups and the lanthanide series. Copper salts are particularly preferred.
Unfortunately, these dyeing processes do not meet the stringent technical and toxicological requirements which hair dyes are expected to satisfy. On the one hand, most metal salts are themselves colored compounds so that they cannot always be prevented from influencing the color obtained. On the other hand, many of the metal salts used are themselves oxidizing agents. However, the most serious disadvantage is that many of the described heavy metal salts are by no means toxicologically safe.
Accordingly, the problem addressed by the present invention was to provide a dye for dyeing keratin fibers, particularly human hair, which would contain indoline derivatives as oxidation dye precursors, which would give intensive colors in a short time without the addition of oxidizing agents and which would only contain toxicologically safe, colorless metal salts as oxidation catalysts, typical heavy metal salts such as, for example, manganese, cobalt, copper or silver salts being ruled out from the outset.